IGBTs are widely used in high-power switching equipment, such as high-voltage DC (HVDC) equipment, including voltage source converters. In such applications, IGBTs are typically combined with a diode arranged in parallel and conducting in the reverse transistor direction (“free wheel diode”).
RC-IGBTs are chips in which a transistor is combined with a diode conducting in the reverse transistor direction. Numerous chip designs have been proposed and used within this concept, which has also been further developed into the bi-mode insulated gate transistor (BIGT). As used herein, the term RC-IGBT covers both conventional RC-IGBTs and BIGTs. The RC-IGBT can be operated both in an IGBT mode (positive collector-emitter current), also referred to as transistor mode or forward mode, and in a diode mode (negative collector-emitter current) also referred to as reverse mode. However, the anode efficiency in the diode mode is dependent on the gate voltage. When the gate is turned off, the anode efficiency in diode mode is high while the anode efficiency is reduced when the gate is turned on. A particular advantage of BIGTs over other RC-IGBT designs is their soft turn-off behaviour in both IGBT and diode mode. It also appears possible to reduce the reverse recovery losses in BIGTs further than in earlier RC-IGBT technology.
Aspects of the gate-emitter voltage control in RC-IGBTs are discussed in an article by Rahimo et al. entitled “A high current 3300 V module employing reverse conducting IGBTs setting a new benchmark in output power capability”, Proceedings of the 20th International Symposium on Power Semiconductor Devices & ICs (18-22 May 2008).